This section provides background information related to the present disclosure which is not necessarily prior art.
As a result of environmental and other concerns, plastic containers (more specifically polyester and even more specifically polyethylene terephthalate (PET) containers) are now being used more than ever to package numerous commodities previously supplied in glass containers. Manufacturers and fillers, as well as consumers, have recognized that PET containers are lightweight, inexpensive, recyclable and manufacturable in large quantities.
Blow-molded plastic containers have become commonplace in packaging numerous commodities. PET is a crystallizable polymer, meaning that it is available in an amorphous form or a semi-crystalline form. The ability of a PET container to maintain its material integrity relates to the percentage of the PET container in crystalline form, also known as the “crystallinity” of the PET container. The following equation defines the percentage of crystallinity as a volume fraction:
      %    ⁢                  ⁢    Crystallinity    =            (                        ρ          -                      ρ            a                                                ρ            c                    -                      ρ            a                              )        ×    100  where ρ is the density of the PET material, ρa is the density of pure amorphous PET material (1.333 g/cc), and ρc is the density of pure crystalline material (1.455 g/cc). Once a container has been blown, a commodity may be filled into the container. Also, in some cases, a preform of the container is formed (e.g., by injection molding), and the commodity is introduced into the preform to expand the preform and simultaneously form and fill the container.